Previous composite polytetrafluoroethylene and elastomer or rubber type lip seals have not been substantially uniform in thickness and have usually been manufactured by being separately molded. That is, the polytetrafluoroethylene washer, wafer or lip-sealing part was fabricated and then each wafer was etched and placed into a mold where the elastomer or rubber for that wafer was molded thereon. The elastomer usually substantially surrounded at least one edge and part of one radial side of the polytetrafluoroethylene wafer, in that to make an abutting edge portion of rubber or elastomer of the same thickness as the polytetrafluoroethylene wafer would be practically impossible without also producing flash or overflow of elastomer at the joint. Furthermore, separately molded seals in multi-cavity molds often are not uniformly formed because they may not receive the same exact charge of elastomer, pressure and/or temperature.
It has always been a problem to make lip seals more flexible and more universal in their use. Also to form a thin section in the elastomeric or rubber portion of a combination lip seal to increase its flexibility, weakens the seal in that rubber fatigues in much less time than polytetrafluoroethylene at elevated temperatures.
Although polytetrafluoroethylene alone or rubber alone has been preformed into tubes and sliced into washers, never before has an elastomer also been formed concentric with polytetrafluoroethylene (PTFE) tube and sliced off therewith to produce a uniform and uniformly thin combination polytetrafluoroethylene and elastomeric wafer lip seal.